Aluminium tube weight calculator
Round tube in aluminium alloy: 10 common sizes with the mass per metre, and a calculator for your own. Aluminium weighs under 35 % of the steel of the same section.
Short answer
The mass of aluminium tube follows from π·t·(D − t)·2.70 g/cm³: a 20×2 mm tube weighs 0.305 kg/m, 30×2 mm weighs 0.475 kg/m and 50×3 mm weighs 1.20 kg/m. A 6 m length of 30×2 mm is therefore about 2.85 kg. Aluminium weighs under 35 % of steel tube of the same section. The masses of common sizes are in the table below.
Common sizes and mass per metre
| Size, mm | Cross-section, mm² | kg/m |
|---|---|---|
| 12×1 | 35 | 0.09 |
| 16×1.5 | 68 | 0.18 |
| 20×2 | 113 | 0.31 |
| 25×2 | 145 | 0.39 |
| 30×2 | 176 | 0.48 |
| 35×2 | 207 | 0.56 |
| 40×2 | 239 | 0.64 |
| 50×3 | 443 | 1.20 |
| 60×3 | 537 | 1.45 |
| 80×3 | 726 | 1.96 |
Where the number comes from
The cross-section works out as F = π/4 · (D² − (D − 2t)²). For 35×2 mm that is 207 mm², which at a density of 2.70 g/cm³ gives 0.56 kg/m.
Aluminium is welded with TIG on alternating current or with a wire feeder and aluminium wire; the oxide film melts at around 2050 °C, far above the metal itself, and has to come off with a stainless brush immediately before welding. The detail is in welding aluminium.
How to work out tube mass by hand
The formula F = π/4 · (D² − (D − 2t)²) subtracts the bore from the full circle. Simplified, it becomes F = π · (D − t) · t: the circumference along the middle of the wall times the wall thickness. Both give the same answer; the second is easier to keep in your head.
Example: 50×3 tube, 6 m length.
- Area: π · (50 − 3) · 3 = π · 141 ≈ 443 mm². Check: π/4 · (2500 − 1936) = π/4 · 564 ≈ 443 mm².
- Mass per metre: 443 × 2.70 / 1000 = 1.196 kg/m.
- A 6 m length: 7.18 kg. A handrail from three lengths is just over 21 kg of tube.
The second form shows that with a thin wall the mass grows almost in proportion to the diameter: a 40×2 tube weighs 0.645 kg/m, a 25×2 0.390 kg/m. Doubling the wall almost exactly doubles the mass — slightly less, because the mean circumference shrinks.
Aluminium versus steel tube
A 50×3 tube weighs 3.477 kg/m in steel and 1.196 kg/m in aluminium, 0.344 of the steel mass. In bending, though, aluminium is three times as flexible (70 000 against 210 000 MPa). The moment of inertia of a thin-walled tube grows with the cube of the diameter but only linearly with the wall, hence the same rule as for box sections:
- three times the wall at the same diameter — mass ≈ 1.03 of steel, the saving disappears;
- about 1.44 times the diameter at the same wall — mass ≈ 0.50 of steel.
A Ø50 steel tube replaced by a Ø70–75 aluminium tube with the same wall deflects about the same and weighs roughly half. Load-bearing members still need a strength check under EN 1999-1-1, not just a deflection check. Steel tube has its own steel tube weight calculator.
Tube alloy and mass
Aluminium tubes are mostly extrusions in 6xxx-series alloys; in the site’s density table 6060 and 6082 are both 2.70 g/cm³, so the table above applies without correction. A 50×3 tube in 5083 (2.66 g/cm³) would weigh 1.178 kg/m, in 7075 (2.81 g/cm³) 1.245 kg/m. A difference of 1.5–4 % matters when a big batch is settled by the kilogram, not for a single structure.
Welding aluminium tube
- Position. A tube that can be rotated is welded in the flat position, turning it continuously — neater and faster than going round a fixed joint. Tube position designations are explained on the welding positions page.
- Clean inside. Brush the oxide off with stainless steel on the inside of the edge too, as far as you can reach; a dirty tube end is a direct route to porosity.
- Filler. For 6xxx alloys the site’s filler table names ER 4043 as more resistant to hot cracking; ER 5356 gives a stronger weld and keeps its colour after anodising, but not above 65 °C.
- 1–2 mm walls. Thin tube burns through easily at the end of the weld, where heat has built up; finish faster or at lower current.
Technique details are in the article on welding aluminium. Square and rectangular sections are on the aluminium box section page, and every shape in the aluminium weight calculator.
Common mistakes with tube
- Nominal size instead of outside diameter. Pipework is sometimes described by nominal size; the formula needs the outside diameter measured with a caliper.
- Inside diameter in the D field. A 50 bore with a 3 mm wall is 56 outside — 12.8 % more mass.
- 1.5 wall instead of 2. On a 16 mm tube that is almost 30 %; check the wall on the cut end, not by eye.
- Tube counted as bar. A Ø50 bar weighs 5.301 kg/m — more than four times a 50×3 tube.
Frequently asked questions
Does the alloy change the weight?
Barely. The density of aluminium alloys runs between 2.66 and 2.80 g/cm³, and trade calculations use 2.70. Across a whole pallet the difference is smaller than the rolling tolerance, so 2.70 is enough for quoting and haulage.
Why does this differ from the weight at the stockist?
Because the dimensional tolerance works both ways, and sheet and section rarely come out at exactly the nominal thickness. On a thin wall the gap reaches a few per cent — order by the tonne with a margin.
How do I work out a tube if I know the inside diameter?
Add two walls to it: D = d + 2t. A tube with a 50 mm bore and a 3 mm wall is a 56×3 tube — it weighs 1.349 kg/m, not 1.196 kg/m like a 50×3. The formula and the calculator take the outside diameter.
Is an aluminium tube stiffer than a round bar of the same mass?
Yes, markedly. The tube’s metal sits far from the axis, where it does most of the work in bending. A 50×3 tube (443 mm²) has about the area of a Ø24 bar but is several times stiffer in bending — which is why frames and handrails use tube, not bar.
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